Intermittent font display problem from LMS

I've created and published a course for my client in Storyline 2, using the National font family. Throughout review stages, there were no issues with how these fonts displayed - we had the module sitting on our FTP site and our client was able to view the course fine. 

Now, the client's LMS provider has uploaded one of the courses and has noticed isolated instances of the font not displaying correctly within the course, viewing it in Chrome. There doesn't seem to be rhyme or reason for it - only one text box on the base layer of a slide is affected, while other text boxes remain unaffected. Also, this happens in only a couple of places in the course - not on every page. Here's an example, showing text boxes that are unaffected as well as one that is (overlapping the cross at the top right). 

Any ideas?